The trend of plant control is directed toward the networked control using a wireless communication or the like in the future. In the networked control, a packet transmission error that the PV or the MV does not reach a destination from a sender due to aggravation of communication circumstances, i.e., a packet loss, occurs. In the network control system, a compensation algorithm for a packet loss is demanded.
FIG. 8 is a functional block diagram showing a configurative example of the network control system in the prior art. As a basic configuration, a plant side 10 and a controller side 20 are connected mutually via a network 30.
The PV is transmitted from a sensor 12, which measures a physical quantity of a controlled object plant 11 on the plant side 10, to a controller 21 on the controller side 20 via the network 30. The controller 21 calculates a deviation between the transmitted PV and the set SV, e.g., a “proportional-intergral-derivative” or PID-operated MV, and transmits this MV to an actuator 13 on the plant side 10 via the network 30. The actuator 13 provides the received MV to the controlled object plant 11.
When the controller 21 cannot receive the PV due to the packet loss, the controller 21 compensates for the PV required for the MV calculation by a PV complementary value provided by a PV complementing unit 22. Similarly, when the actuator 13 cannot receive the PV due to the packet loss, the actuator 13 compensates for the MV, which is to be provided to the controlled object plant 11, by an MV complementary value provided by an MV complementing unit 14.
As the PV complementary value and the MV complementary value, the latest PV and MV values received in the sampling period immediately before the packet loss occurs or the estimated values calculated based on trend data in predetermined sampling periods are employed.
Patent Document 1: JP-A-08-328650
Patent Document 2: JP-A-11-345003
Patent Document 3: JP-A-2002-040917
Patent Document 4: JP-A-2006-277306
Patent Document 5: JP-A-2007-233891